Method for generating an output signal having predetermined jitter characteristics

ABSTRACT

A method for generating an output signal having predetermined jitter characteristics is disclosed. A first signal is generated via a first signal generator module. A second signal is generated via a second signal generator module. The first signal is pulse position modulated by the second signal, thereby generating a modulated signal having predetermined jitter characteristics. An output signal having predetermined jitter characteristics is generated based on the modulated signal. Moreover, a signal generator for generating an output signal having predetermined jitter characteristics is disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/799,601, filed Jan. 31, 2019, the disclosure of which is incorporatedherein in its entirety.

FIELD OF THE DISCLOSURE

Embodiments of the present disclosure relate generally to a method forgenerating an output signal having predetermined jitter characteristicsas well as to a signal generator for generating an output signal havingpredetermined jitter characteristics.

BACKGROUND

With increasing data rates, the demands on communication devicesregarding maximum generated jitter and/or jitter tolerance areconstantly on the rise.

For some applications, e.g. for jitter tolerance testing of a deviceunder test, a test signal having predefined jitter characteristics isneeded. Such test signals are often generated via arbitrary waveformgenerators (AWGs).

These AWGs usually employ a software-based signal generation, whereinthe test signal having the predetermined jitter characteristics isgenerated based upon one or several parameters that are loaded by thesoftware, and the test signal is then generated based on theseparameters.

However, such AWGs are not capable of changing the jittercharacteristics of the test signal in real time, as a change of thejitter characteristics implies changing parameters of the AWG, whichhave to be reloaded by the software first.

Thus, there is a need for a method as well as for a signal generator forgenerating an output signal having predetermined jitter characteristicsthat are capable of a faster adaption of the jitter characteristics.

SUMMARY

Embodiments of the present disclosure provide a method for generating anoutput signal having predetermined jitter characteristics. In anembodiment, a first signal is generated via a first signal generatorcircuit or module. A second signal is generated via a second signalgenerator circuit or module. The first signal is pulse positionmodulated by the second signal, thereby generating a modulated signalhaving predetermined jitter characteristics. An output signal havingpredetermined jitter characteristics is generated based on the modulatedsignal.

The disclosure is based on the rationale to use pulse positionmodulation of the first signal by the second signal instead ofgenerating the output signal directly via an AWG. In other words, thefirst signal is the carrier signal of the modulation and the secondsignal is the modulating signal.

By employing this pulse-position modulation approach, the predeterminedjitter characteristics can be set and/or modified by setting and/ormodifying the first signal and/or the second signal, for example thesecond signal. This way, the predetermined jitter characteristics can beadapted in real time or at least with a delay that is in the order ofmagnitude of a symbol period of the output signal. For example, thedelay is smaller than ten times the symbol period, for example smallerthan five times the symbol period.

Thereby and in the following, the term “predetermined jittercharacteristics” is understood to include both the total jittercontained in the respective signal and the individual jitter componentscontained in the respective signal. The modulated signal and the outputsignal each contain periodic jitter (PJ), random jitter (RJ), datadependent jitter (DDJ) and/or other bounded uncorrelated jitter (OBUJ).In some embodiments, the modulated signal and the output signal may eachcontain inter-symbol interferences (ISI) and/or duty cycle distortion(DCD).

Moreover, it is to be understood that the output signal may be identicalwith the modulated signal. Alternatively, the modulated signal may befurther processed in order to generate the output signal based on themodulated signal.

According to one embodiment of the disclosure, the first signal is PAM-ncoded, wherein n is an integer greater than 1. Accordingly, the methodis not limited to binary signals (PAM-2 coded signals) since any kind ofpulse-amplitude modulated signals may be generated and/or processed.Thus, the first signal comprises a sequence of symbols (bits in thePAM-2 coded case) that are generated via the first signal generatormodule. Each symbol takes one of n possible values, wherein signal edgesare located between adjoining symbols having different values. Thesignal edges connect the individual symbols in a continuous andapproximately linear manner, i.e. the signal edges each have a certainslope.

According to a further embodiment of the disclosure, the first signal isgenerated with rising edges having predefined rising slopes betweenpairs of different signal levels and with falling edges havingpredefined falling slopes between pairs of different signal levels inorder to obtain a predefined duty cycle distortion in the modulatedsignal. In total, there are n*(n−1) possible transitions between thedifferent signal levels and, in general, the slopes or more preciselythe absolute values of the slopes corresponding to each of thetransitions may all be different from each other. However, at least someof the slopes may be pairwise equal to each other.

In the case of a PAM-2 coded signal, there are two different levels“low” and “high” and thus two possible transitions, namely “low to high”and “high to low”. Therefore, in order to introduce a duty cycledistortion in this case, the slope of the signal edge corresponding tothe transition “low to high”, i.e. the rising slope, may be chosen to bedifferent from the slope of the signal edge corresponding to thetransition “high to low”, i.e. the falling slope. Thus, in the case of aPAM-2 coded signal, the first signal has a trapezoidal shape.

Thereby and in the following, it is to be understood that the slope of arising edge between two signal levels and the corresponding slope of thefalling edge between the same two signal levels are considered to beequal if their absolute values are equal and are considered differentfrom each other if their absolute values are different from each other.

According to one aspect of the disclosure, the first signal comprises atleast one of a predefined symbol sequence and a pseudo-random symbolsequence. In some embodiments, in the case of the first signal beingPAM-2 coded, the first signal comprises at least one of a predefined bitsequence and a pseudo-random bit sequence. The corresponding symbolsequence or bit sequence may be loaded into the first signal generatormodule from a memory circuit of the signal generator and/or may bereceived from an external signal source.

The pulse position of each signal edge of the first signal may bemodulated, wherein the modulation is kept constant within each symbol.In other words, only the temporal position of each of the signal edgesis adjusted while no changes are made within the symbol itself or to therespective slopes of the signal edges. Put differently, the temporallength of a symbol is only modified by shifting the signal edgesdefining the respective symbol and not by contracting or stretchingareas within the symbol itself.

According to another aspect of the disclosure, the modulated signal isfiltered via a filter in order to generate the output signal, therebygenerating predefined inter-symbol interferences in the output signal.The inter-symbol interferences are part of the data dependent jitter andusually depend on certain characteristics of a transmission channelthrough which a signal is sent. Accordingly, defining parameters of thefilter are chosen such that the filter reflects the transmissionchannel's transmission characteristics. This way, also the inter-symbolinterference component of the total jitter is taken into account in theoutput signal in a particularly convenient fashion.

In another embodiment of the disclosure, the filter is a finite impulseresponse filter. For example, the filter is established as a low passfilter. Such a low-pass filter reflects the transmission characteristicsof a finite-bandwidth medium such as a cable and therefore reproducesthe inter-symbol interferences caused by the finite-bandwidth medium.

According to one aspect of the disclosure, the modulated signal isfiltered with a filter sampling rate being equal to or larger than adata rate of the first signal. This way, a higher frequency resolutionof the filter is provided as, in general, the frequency resolutionincreases with the filter sampling rate.

In another embodiment of the disclosure, the second signal comprises atleast one of a periodic signal and white Gaussian noise in order togenerate periodic jitter and random jitter in the modulated signal,respectively. In general, the periodic signal may have an arbitrary, butof course periodic shape. In the simplest case, the periodic signal isestablished as a sine-shaped signal with a certain amplitude and phase.Via the periodic signal, the periodic jitter component is imprinted onthe first signal, such that the modulated signal comprises periodicjitter. More precisely, because the first signal is pulse-positionmodulated by second signal and the second signal comprises a periodicsignal, the result of this modulation (the modulated signal) comprisesperiodic jitter. Similarly, the white Gaussian noise contained in thesecond signal imprints random jitter on the first signal, such that themodulated signal comprises random jitter. By adjusting an expectationvalue and/or a variance of the white Gaussian noise, an expectationvalue and/or a variance of the random jitter may be modified.

The periodic signal may be generated as a superposition of severalsine-shaped signals. As every periodic function can be decomposed into asum of sine- and cosine-functions, i.e. as a Fourier series, anarbitrary periodic shape of the periodic signal can be achieved thisway. Put differently, an arbitrary periodic jitter component in themodulated signal and thus in the output signal can be generated by thesuperposition of several sine-shaped signals in the second signal.

According to a further aspect of the disclosure, a perturbation signalbeing uncorrelated with the first signal, the second signal and themodulated signal is generated and/or received, wherein the perturbationsignal is added to the first signal, the second signal and/or themodulated signal in order to generate other bounded uncorrelated jitterin the output signal. To which of the signals the perturbation signal isadded depends on the place where another, uncorrelated data stream wouldcouple to a data signal transmitted to or received from a device undertest. In other words, the place of coupling is highly dependent on thespecific test conditions and the characteristics of the particulardevice under test.

In another embodiment of the disclosure, the perturbation signal ismultiplied with a predetermined weighting factor before being added tothe at least one of the first signal, the second signal and themodulated signal. In this way, different coupling strengths of theperturbation signal can be modelled.

In some embodiments, at least the modulated signal is established as adigital signal, and the modulated signal is converted to an analogsignal in order to generate the output signal. In some embodiments, thefirst signal and/or the second signal may be established as digitalsignals as well.

With the method according to the disclosure, the individual jittercomponents described above can be added to the output signalindividually and independently from each other. Put differently, eachjitter component can be adjusted separately such that the methodprovides maximum flexibility for adjusting the total jitter and/or theindividual components of the total jitter contained in the outputsignal.

Embodiments of the present disclosure further provide a signal generatorfor generating an output signal having predetermined jittercharacteristics, comprising a first signal generator circuit or module,a second signal generator circuit or module and a modulation circuit ormodule. The first signal generator module is configured to generate afirst signal and to forward the first signal to the modulation module.The second signal generator module is configured to generate a secondsignal and to forward the second signal to the modulation module. Themodulation module is configured to pulse-position modulate the firstsignal by the second signal, thereby generating a modulated signalhaving predetermined jitter characteristics.

The disclosure is based on the rationale to use the pulse-positionmodulation of the first signal by the second signal instead ofgenerating the output signal directly via an AWG. In other words, thefirst signal is the carrier signal of the modulation and the secondsignal is the modulating signal.

By employing this pulse-position modulation approach, the predeterminedjitter characteristics can be set and/or modified by setting and/ormodifying the first signal and/or the second signal, for example thesecond signal. This way, the predetermined jitter characteristics can beadapted in real time or at least with a delay that is in the order ofmagnitude of a symbol period of the output signal. For example, thedelay is smaller than ten times the symbol period, for example smallerthan five times the symbol period.

In some embodiments, the signal generator is configured to perform theabove-described method for generating an output signal havingpredetermined jitter characteristics.

Regarding the further advantages, reference is made to the explanationsgiven above with regard to the method for generating an output signalhaving predetermined jitter characteristics.

In some embodiments, the modulation module may be part of the firstsignal generator module. In this particular embodiment, the secondsignal generator module is configured to forward the second signal tothe first signal generator module, more precisely to the modulationmodule comprised within the first signal generator module.

According to one aspect of the disclosure, the first signal generatormodule is configured to generate the first signal as a PAM-n codedsignal with rising edges having predefined rising slopes between pairsof different signal levels and with falling edges having predefinedfalling slopes between pairs of different signal levels in order toobtain a predefined duty cycle distortion in the modulated signal. Intotal, there are n*(n−1) possible transitions between the differentsignal levels and, in general, the first signal generator module isconfigured to generate the first signal in such a way that the slopes ormore precisely the absolute values of the slopes corresponding to eachof the transitions all can be different from each other, although forexample the slopes may be pairwise equal.

In the case of a PAM-2 coded signal, there are two different levels“low” and “high” and thus two possible transitions, namely “low to high”and “high to low”. Therefore, in order to introduce a duty cycledistortion in this case, the slope of the signal edge corresponding tothe transition “low to high” may be chosen to be different from theslope of the signal edge corresponding to the transition “high to low”.Thus, in the case of a PAM-2 coded signal, the first signal generatormodule is configured to generate the first signal with a trapezoidalshape.

In another embodiment of the disclosure, the second signal generatormodule is configured to generate the second signal with a periodicsignal and/or white Gaussian noise. In general, the periodic signal mayhave an arbitrary, but of course periodic shape. In the simplest case,the periodic signal is established as a sine-shaped signal with acertain amplitude and phase.

Via the periodic signal, the periodic jitter component is imprinted onthe first signal, such that the modulated signal comprises periodicjitter. More precisely, because the first signal is pulse-positionmodulated by second signal and the second signal comprises a periodicsignal, the result of this modulation (the modulated signal) comprisesperiodic jitter. Similarly, the white Gaussian noise contained in thesecond signal imprints random jitter on the first signal, such that themodulated signal comprises random jitter. By adjusting an expectationvalue and/or a variance of the white Gaussian noise, an expectationvalue and/or a variance of the random jitter may be modified.

The signal generator may comprise a finite impulse response filterdownstream of the modulation module. Defining parameters of the impulseresponse filter are such that the filter reflects the transmissioncharacteristics of a transmission channel to be modelled by the finiteimpulse response filter. This way, also the inter-symbol interferencecomponent of the total jitter is taken into account in the outputsignal.

For example, the filter is established as a low pass filter. Such alow-pass filter reflects the transmission characteristics of afinite-bandwidth medium such as a cable and therefore reproduces theinter-symbol interferences caused by the finite-bandwidth medium.

According to a further aspect of the disclosure, the signal generatorcomprises a perturbation circuit or module being configured to generateand/or receive a perturbation signal that is uncorrelated with the firstsignal, the second signal and the modulated signal, wherein theperturbation module is configured to add the weighted perturbationsignal to at least one of the first signal, the second signal and themodulated signal. In this way, different coupling strengths of theperturbation signal can be modelled.

At least one of the first signal generator module and the second signalgenerator module may be established as a digital signal generatorcircuit.

In some embodiments, the signal generator comprises a digital-to-analogconverter downstream of the modulation module.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of theclaimed subject matter will become more readily appreciated as the samebecome better understood by reference to the following detaileddescription, when taken in conjunction with the accompanying drawings,wherein:

FIG. 1 shows a block diagram of a representative signal generatoraccording to a first embodiment of the disclosure;

FIG. 2 shows a block diagram of a representative signal generatoraccording to a second embodiment of the disclosure;

FIG. 3 shows a schematic flow chart of a representative method accordingto an embodiment of the disclosure;

FIG. 4 shows a block diagram of a representative modulation module of asignal generator according to FIG. 1 and/or FIG. 2;

FIG. 5 shows a schematic flow chart of a representative method accordingto an embodiment of the disclosure, and

FIG. 6 shows a detailed illustration of Step S3 of the method accordingto FIG. 5.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings, where like numerals reference like elements, is intended as adescription of various embodiments of the disclosed subject matter andis not intended to represent the only embodiments. Each embodimentdescribed in this disclosure is provided merely as an example orillustration and should not be construed as preferred or advantageousover other embodiments. The illustrative examples provided herein arenot intended to be exhaustive or to limit the claimed subject matter tothe precise forms disclosed.

FIG. 1 shows a block diagram of a signal generator 10 for generating anoutput signal x_(out)(t) having predetermined jitter characteristics.Such output signals having predetermined jitter characteristics areusually employed for testing certain properties of a device under test,for example for jitter tolerance testing of the device under test.

Thereby and in the following, the term “predetermined jittercharacteristics” is understood to include both the total jittercontained in the respective signal and the individual jitter componentscontained in the respective signal. The modulated signal and the outputsignal each contain periodic jitter (PJ), random jitter (RJ), datadependent jitter (DDJ) and/or other bounded uncorrelated jitter (OBUJ).In some embodiments, the modulated signal and the output signal may eachcontain inter-symbol interferences (ISI) and/or duty cycle distortion(DCD).

The signal generator 10 comprises a first signal generator circuit ormodule 12, a second signal generator circuit or module 14, a modulationcircuit or module 16, a filter 18, a perturbation circuit or module 20and a memory 21.

The first signal generator module 12 and the second signal generatormodule 14 are both connected to the modulation module 16 upstream of themodulation module 16. Accordingly, signals can be sent from both thefirst signal generator module 12 and the second signal generator module14 to the modulation module 16.

The filter 18 is connected to the modulation module 16 downstream of themodulation module 16 such that signals sent by the modulation module 16are received by the filter 18.

The perturbation module 20 is connected to the filter 18 downstream ofthe filter 18 and comprises a perturbation signal generator 22, aweighting circuit or unit 24 and an adding circuit or unit 26.

However, the perturbation module 20 may also be connected to the boththe modulation module 16 and the filter 18 downstream of the modulationmodule 16 and upstream of the filter 18.

Alternatively, the perturbation module 20 may be connected to themodulation module 16, the first signal generator module 12 or the secondsignal generator module 14 upstream of the modulation module 16.Further, the perturbation module 20 may be connected downstream of thefirst signal generator module 12 or the second signal generator module14, respectively.

FIG. 2 shows another embodiment of the signal generator 10. Thisembodiment differs from the embodiment of FIG. 1 in that the modulationmodule 16 is part of the first signal generator module 12 rather thanbeing established separately from the first signal generator module 12.The remaining parts of the signal generator 10, however, remainunchanged compared to the embodiment of FIG. 1.

The signal generator 10 according to the embodiments of FIGS. 1 and 2 isconfigured to perform a method for generating an output signal havingpredetermined jitter characteristics, which method is described in thefollowing with reference to FIG. 3.

A first signal x₁(t) is generated via the first signal generator (stepS1). The shape of the first signal x₁(t) is schematically depicted inFIG. 4.

The first signal x₁(t) is a digital PAM-n coded signal, wherein n is aninteger bigger than one. Thus, the first signal x₁(t) comprises asequence of symbols (bits in the PAM-2 coded case) that are generatedvia the first signal generator module 12.

The sequence comprised in the first signal x₁(t) is at least one ofpredefined and pseudo-random, and is either generated by the firstsignal generator module 12 itself or loaded into the first signalgenerator module 12 from the memory 21.

Each symbol takes one of n possible values, wherein signal edges arelocated between adjoining symbols having different values. The signaledges connect the individual symbols in a continuous and approximatelylinear manner, i.e. the signal edges each have a certain slope.

The first signal x₁(t) is generated with rising edges having predefinedrising slopes between pairs of different signal levels and with fallingedges having predefined falling slopes between pairs of different signallevels such that the first signal x₁(t) has a predefined duty cycledistortion.

In total, there are n*(n−1) possible transitions between the differentsignal levels and, in general, the slopes or more precisely the absolutevalues of the slopes corresponding to each of the transitions may aredifferent from each other. However, at least some of the slopes may bepairwise equal to each other.

In some embodiments, all slopes may be equal to each other, such thatthe first signal x₁(t) has no duty cycle distortion in this case.

Thereby and in the following, it is to be understood that the slope of arising edge between two signal levels and the corresponding slope of thefalling edge between the same two signal levels are considered to beequal if their absolute values are equal and are considered differentfrom each other if their absolute values are different from each other.

In the case of a PAM-2 coded signal, there are two different levels“low” and “high” and thus two possible transitions, namely “low to high”and “high to low”. Therefore, in order to introduce a duty cycledistortion in this case, the slope of the signal edge corresponding tothe transition “low to high” is chosen to be different from the slope ofthe signal edge corresponding to the transition “high to low”. Thus, inthe case of a PAM-2 coded signal, the first signal has a trapezoidalshape. Accordingly, the first signal generator module 12 is establishedas a trapezoid generator.

Moreover, a digital second signal x₂(t) is generated via the secondsignal generator (step S2). The second signal x₂(t) comprises at leastone of a periodic signal and white Gaussian noise.

In general, the periodic signal has an arbitrary periodic shape, whichshape may be set by a user of the signal generator 10 or may be loadedfrom the memory 21.

In the simplest case, the periodic signal portion of the second signalx₂(t) is established as a sine-shaped signal with a certain amplitudeand phase.

In general, the periodic signal portion of the second signal x₂(t) isgenerated as a superposition of several sine-shaped signals. Thus, thesecond signal x₂(t) has the following general form:

${x_{2}(t)} = {{\sum\limits_{k = 0}^{N}{A_{k}{\sin\left( {{\omega_{k} \cdot t} + \theta_{k}} \right)}}} + {x_{GN}.}}$

Therein, A_(k) are the amplitudes of the individual sine-shaped periodicsignal portions, Ω_(k) are their frequencies and θ_(k) their phases,thus the sum in the equation above essentially represents a Fourierseries of a periodic signal to be obtained. x_(GN) represents the whiteGaussian noise portion of the second signal x₂(t), and is usuallynormal-distributed with a certain expected value and a certain variance.

Now, the first signal x₁(t) and the second signal x₂(t) are forwarded tothe modulation module 16 and the first signal x₁(t) is phase positionmodulated by the second signal x₂(t), thereby generating a modulatedsignal x_(mod)(t) (step S3). More precisely, the first signal x₁(t) isthe carrier signal of the modulation and the second signal x₂(t) is themodulating signal of the modulation.

As is illustrated in FIG. 5 for the case of a PAM-2 coded signal, theposition of each signal edge of the first signal x₁(t) is shifted basedon the value of the second signal x₂(t) at a certain time, which certaintime is equal to the temporal position of the preceding signal edge ofthe first signal x₁(t), as indicated by the arrows in FIG. 5. Thus, thetemporal position t_(i) of the i-th signal edge is shifted by a timespan Δ_(t), as a result of the pulse position modulation.

The modulation is kept constant within each symbol. In other words, onlythe temporal position of each of the signal edges is adjusted while nochanges are made within the symbol itself. In some embodiments, nochanges are made to the slopes of the signal edges. Put differently, thetemporal length of a symbol is only modified by parallel shifting of thesignal edges defining the respective symbol and not by contracting orstretching areas within the symbol itself.

Step S3 is illustrated in more detail in FIG. 6. The modulation module16 samples the first signal x₁(t) having a data rate f_(d) with asampling frequency f_(s). Moreover, the modulation module 16 alsosamples the modulation signal via a first sample and hold circuit ormember S&H1.

The modulation module 16 now detects signal edges in the first signalx₁(t) and controls the first sample and hold member S&H1 based onwhether a signal edge is detected or not (edge detect).

If no signal edge is detected, only the first signal x₁(t) is forwardedto a second sample and hold circuit or member S&H2. Thus, if no signaledge is detected, the corresponding portion of the first signal x₁(t)remains unchanged.

If a signal edge is detected, the first signal x₁(t) is forwarded to thesecond sample and hold member S&H2. Moreover, the current value of thesecond signal x₂(t) is scaled based on at least one jitter factor ΔJ andforwarded to the second sample and hold member S&H2. The at least onejitter factor ΔJ may be preset by a user and/or may be loaded from thememory 21.

More precisely, phases φ_(PJ) _(k) (i) and φ_(RJ)(i) are determined forthe periodic signal components and the white Gaussian noise component ofthe second signal x₂(t) and scaled by respective jitter factors, suchthat an overall phase shift Δφ_(tot) is determined to be

${{\Delta\varphi}_{tot}(i)} = {{\sum\limits_{k = 0}^{N}{\Delta J_{{PJ}_{k}}{\varphi_{{PJ}_{k}}(i)}}} + {\Delta J_{RJ}{{\varphi_{RJ}(i)}.}}}$

This overall phase shift Δφ_(tot) is then added to the phase of thecorresponding signal edge number i, such that the temporal position ofthe signal edge number i is shifted when output by the second sample andhold member S&H2.

As a result of the steps S1 to S3, the modulated signal x_(mod)(t)contains the duty cycle distortion inherited from the first signalx₁(t), periodic jitter due to the periodic signal portions of the secondsignal x₂(t) and random jitter due to the white Gaussian noise portionof the second signal x₂(t).

The modulated signal x_(mod)(t) is then forwarded to the filter 18 andfiltered via the filter 18, thereby generating a filtered modulatedsignal x_(mod,filt)(t) having predefined inter-symbol interferences.

In general, defining parameters of the filter 18 are chosen such thatthe filter 18 reflects the characteristics of a transmission channelthat is to be modelled.

The filter 18 may be established as a finite impulse response filter.For example, the filter 18 is established as a low pass filter. Such alow-pass filter reflects the transmission characteristics of afinite-bandwidth medium such as a cable and therefore reproduces theinter-symbol interferences caused by the finite-bandwidth medium.

In some embodiments, a filter sampling rate may be chosen to be equal toor larger than a data rate of the first signal x₁(t).

Moreover, a perturbation signal x_(per)(t) is generated and/or receivedby the perturbation signal generator 22, weighted with a weightingfactor g by the weighting unit 24 and added to the filtered modulatedsignal X_(mod,filt)(t) by the adding unit 26, thereby generating theoutput signal x_(out)(t) (step S5).

Thereby, the perturbation signal x_(per)(t) and the weighting factor arechosen such that a predetermined other bounded uncorrelated jitter isadded to the filtered modulated signal X_(mod,filt)(t) and thuscomprised in the output signal x_(out)(t).

Accordingly, the form of the perturbation signal x_(per)(t) and/or theweighting factor may be adjustable by a user and/or loaded from thememory 21.

Finally, the output signal x_(out)(t) the output signal x_(out)(t) maybe converted to an analog signal via a digital-to-analog converter if ananalog signal is required for testing the particular device under test(step S6).

As a result of the method described above, the output signal x_(out)(t)comprises predetermined jitter characteristics. More precisely, theoutput signal x_(out)(t) comprises a predetermined duty cycledistortion, a predetermined periodic jitter, a predetermined randomjitter, a predetermined other bounded uncorrelated jitter andpredetermined inter-symbol interferences.

Certain embodiments disclosed herein utilize circuitry (e.g., one ormore circuits) in order to implement protocols, methodologies ortechnologies disclosed herein, operably couple two or more components,generate information, process information, analyze information, generatesignals, encode/decode signals, convert signals, transmit and/or receivesignals, control other devices, etc. Circuitry of any type can be used.

In an embodiment, circuitry includes, among other things, one or morecomputing devices such as a processor (e.g., a microprocessor), acentral processing unit (CPU), a digital signal processor (DSP), anapplication-specific integrated circuit (ASIC), a field-programmablegate array (FPGA), a system on a chip (SoC), or the like, or anycombinations thereof, and can include discrete digital or analog circuitelements or electronics, or combinations thereof. In an embodiment,circuitry includes hardware circuit implementations (e.g.,implementations in analog circuitry, implementations in digitalcircuitry, and the like, and combinations thereof).

In an embodiment, circuitry includes combinations of circuits andcomputer program products having software or firmware instructionsstored on one or more computer readable memories that work together tocause a device to perform one or more protocols, methodologies ortechnologies described herein. In an embodiment, circuitry includescircuits, such as, for example, microprocessors or portions ofmicroprocessor, that require software, firmware, and the like foroperation. In an embodiment, circuitry includes an implementationcomprising one or more processors or portions thereof and accompanyingsoftware, firmware, hardware, and the like.

The present application may reference quantities and numbers. Unlessspecifically stated, such quantities and numbers are not to beconsidered restrictive, but exemplary of the possible quantities ornumbers associated with the present application. Also in this regard,the present application may use the term “plurality” to reference aquantity or number. In this regard, the term “plurality” is meant to beany number that is more than one, for example, two, three, four, five,etc. The terms “about,” “approximately,” “near,” etc., mean plus orminus 5% of the stated value. For the purposes of the presentdisclosure, the phrase “at least one of A and B” is equivalent to “Aand/or B” or vice versa, namely “A” alone, “B” alone or “A and B.”.Similarly, the phrase “at least one of A, B, and C,” for example, means(A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C),including all further possible permutations when greater than threeelements are listed.

The principles, representative embodiments, and modes of operation ofthe present disclosure have been described in the foregoing description.However, aspects of the present disclosure which are intended to beprotected are not to be construed as limited to the particularembodiments disclosed. Further, the embodiments described herein are tobe regarded as illustrative rather than restrictive. It will beappreciated that variations and changes may be made by others, andequivalents employed, without departing from the spirit of the presentdisclosure. Accordingly, it is expressly intended that all suchvariations, changes, and equivalents fall within the spirit and scope ofthe present disclosure, as claimed.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method for generatingan output signal having predetermined jitter characteristics, comprisingthe following steps: generating a first signal via a first signalgenerator; generating a second signal via a second signal generator;pulse-position modulating the first signal by the second signal, therebygenerating a modulated signal having predetermined jittercharacteristics; and generating an output signal having predeterminedjitter characteristics based on the modulated signal.
 2. The method ofclaim 1, wherein the first signal is PAM-n coded.
 3. The method of claim2, wherein the first signal is generated with rising edges havingpredefined rising slopes between pairs of different signal levels andwith falling edges having predefined falling slopes between pairs ofdifferent signal levels in order to obtain a predefined duty cycledistortion in the modulated signal.
 4. The method of claim 2, whereinthe first signal comprises at least one of a predefined symbol sequenceand a pseudo-random symbol sequence.
 5. The method of claim 2, whereinthe pulse position of each signal edge of the first signal is modulated,wherein the modulation of the first signal by the second signal is keptconstant within each symbol.
 6. The method of claim 1, wherein themodulated signal is filtered via a filter in order to generate theoutput signal, thereby generating predefined inter-symbol interferencesin the output signal.
 7. The method of claim 6, wherein the filter is afinite impulse response filter.
 8. The method of claim 6, wherein themodulated signal is filtered with a filter sampling rate being equal toor larger than a data rate of the first signal.
 9. The method of claim8, wherein the periodic signal is generated as a superposition ofseveral sine-shaped signals.
 10. The method of claim 1, wherein thesecond signal comprises at least one of a periodic signal and whiteGaussian noise in order to generate periodic jitter and random jitter inthe modulated signal, respectively.
 11. The method of claim 1, wherein aperturbation signal being uncorrelated with the first signal, the secondsignal and the modulated signal is at least one of generated andreceived, wherein the perturbation signal is added to at least one ofthe first signal, the second signal and the modulated signal in order togenerate other bounded uncorrelated jitter in the output signal. 12.Method according to claim 11, wherein the perturbation signal ismultiplied with a predetermined weighting factor before being added tothe at least one of the first signal, the second signal and themodulated signal.
 13. The method of claim 1, wherein at least themodulated signal is established as a digital signal, and wherein themodulated signal is converted to an analog signal in order to generatethe output signal.
 14. A signal generator for generating an outputsignal having predetermined jitter characteristics, comprising a firstsignal generator circuit, a second signal generator circuit, and amodulation circuit, the first signal generator circuit being configuredto generate a first signal and to forward said first signal to themodulation circuit; the second signal generator circuit being configuredto generate a second signal and to forward said second signal to themodulation circuit; and the modulation circuit being configured topulse-position modulate the first signal by the second signal, therebygenerating a modulated signal having predetermined jittercharacteristics.
 15. The signal generator of claim 14, wherein the firstsignal generator circuit is configured to generate the first signal as aPAM-n coded signal with rising edges having predefined rising slopesbetween pairs of different signal levels and with falling edges havingpredefined falling slopes between pairs of different signal levels inorder to obtain a predefined duty cycle distortion in the modulatedsignal.
 16. The signal generator of claim 14, wherein the second signalgenerator circuit is configured to generate the second signal with atleast one of a periodic signal and white Gaussian noise.
 17. The signalgenerator of claim 14, comprising a finite impulse response filtermodule downstream of the modulation circuit.
 18. The signal generator ofclaim 14, comprising a perturbation circuit being configured to at leastone of generate and receive a perturbation signal that is uncorrelatedwith the first signal, the second signal and the modulated signal,wherein the perturbation module is configured to add the weightedperturbation signal to at least one of the first signal, the secondsignal and the modulated signal.
 19. The signal generator of claim 14,wherein at least one of the first signal generator circuit and thesecond signal generator circuit is established as a digital signalgenerator.
 20. The signal generator of claim 19, comprising adigital-to-analog converter downstream of the modulation circuit.